Hydraulically efficient ribbed pipe having openings

ABSTRACT

A hydraulically efficient metal pipe particularly adapted for use in storm drain and sanitary sewer applications which is adapted for use with a self-supporting interior inert protective lining. The pipe has a channeled wall defining a plurality of outwardly projecting structural ribs and a hydraulically smooth interior surface. The ribs are preferably of a helical configuration and the channels which are formed interiorly thereof are generally either square or rectangular in cross-section and are open along the interior surface of the pipe. The walls defining the ribs can be tapered inwardly to form triangular-shaped channels so as to define an anchor throughout the length of the pipe for securing thereto a smooth interior lining of corrosion-resistant protective material.

This application is a continuation of Ser. No. 718,333 filed on Jun. 18,1991 now abandoned, which is a division of 566,119 filed Aug. 9, 1990now abandoned, which is a division of 352,411 filed May 16, 1989, nowU.S. Pat. No. 4,964,440 which is a division of 260,816 filed Oct. 21,1988 now U.S. Pat. No. 4,838,317.

BACKGROUND OF THE INVENTION

The present invention relates-to pipe for use in sewers, storm drains,penstocks, culverts and other low head applications, and moreparticularly to a hydraulically efficient pipe which is also adapted foruse with an interior inert protective lining without the need foradditional securement means.

Corrugated metal pipe of both the annular and helical type is currentlywidely used for culverts and other similar pipelines due to itsrelatively low cost and light weight which facilitates handling.However, its corrugated construction and susceptibility to corrosionhave heretofore greatly restricted its use in storm drains and preventedaltogether the use of corrugated metal pipe in sanitary applicationssuch as sewer installations. Consequently, industry has been forced toturn to the considerably heavier and more expensive concrete pipe forsuch pipelines.

The cylindrical wall of corrugated pipe is sinusoidal in cross-sectiongiving the pipe a rough interior surface which has a direct adverseeffect on fluid flow therethrough. This effect is clearly illustrated byManning's Equation: ##EQU1## wherein "n" represents the coefficient ofroughness, V represents the velocity of flow in feet per second, thehydraulic radius and S the slope or grade. Smooth concrete pipe has acoefficient of roughness of about 0.013 as opposed to about 0.027 forcorrugated pipe having 3×1.0 inch corrugations and 0.024 for pipe havingcorrugations of 2.66×0.5 inch. Due to this inverse effect on thevelocity of fluid flow, the use of corrugated pipe requires a largerdiameter for a given flow than pipe with a relatively smooth interiorsuch as concrete pipe and the larger the pipe (generally necessitatinglarger corrugations or heavier wall thickness for additional structuralstrength), the greater the difference. It would therefore be desirableto provide a type of pipe having the cost and weight advantages ofcorrugated steel pipe, but with improved hydraulic efficiency.

In addition to having poor fluid flow characteristics, metal corrugatedpipe is highly susceptible to corrosion from the material flowingtherethrough. Accordingly, the steel from which such pipe is made isalmost always galvanized. In some cases an inert protective coating isalso applied to the interior of the pipe in an effort to provideadditional protection against corrosion. However, such coatings havealso proved ineffective in many installations as the turbulent fluidflow through such pipe caused by its rough interior surface causesdebris such as rocks and the like to be dragged or rolled along thesinusoidal corrugations abrading these protective coatings resulting inerosion and corrosion and pipe damage. In an effort to prevent sucherosion and corrosion, the interior of corrugated steel pipe has beenlined with concrete in the hopes that a thicker lining would be moreabrasion resistant and thereby resist deterioration and corrosion. Inaddition, the smooth interior surface presented by the concrete wouldimprove the hydraulic efficiency of the pipe. However, there is nosuitable means for anchoring the concrete to the interior wall ofcorrugated pipe and pieces of the concrete lining inevitably begin tofall therefrom. This destroys the improved flow characteristics of thepipe and when combined with the continual abrading action occurringtherein, quickly destroys the protective concrete layer as well. If aconcrete liner or other suitable material could be adequately anchoredto the pipe wall, the resulting combination would not only be highlysuited for use in storm drains but would be markedly improved over theconventional concrete pipe due to reduced costs and weight.

In addition to accelerating corrosion by causing abrasion of the metal'sprotective coatings, a corrugated surface also causes a build-up orcollection of foreign material on the corrugations. Such a build-up alsoleads to corrosion and, in fact, prevents such pipe from being used insewers or sanitary applications where bacterial build-up can occur. Insuch uses it is necessary to employ pipe having a relatively smoothbore, not solely from a hydraulic standpoint, but to facilitate cleaningof the interior of the pipe and prevent the breeding of bacteria. Hereagain, industry has had to turn to concrete pipe despite the fact thatconcrete is highly susceptible to attack by sulfuric acid which iscreated by the hydrogen sulfide generated in sewer lines. For sewerinstallations as well as storm drains, it would be highly desirable tobe able to utilize the less expensive and lighter steel pipe with aninert interior protective lining. While concrete would not be preferablefor such applications, as above indicated, an inert lining such as oneconstructed of polymer materials such as polyethylene or PVC, whichwould resist the attack of sulfuric acid as well as other forms ofcorrosion, would be ideal. In addition, such a liner should besufficiently thick to provide protection against abrasion. Because theconventional interior linings of corrugated pipe are so susceptible toabrasion and corrosion and a thicker and more abrasive resistant inertlining such as one constructed of concrete or an inert polymer materialcannot be effectively anchored to the corrugated pipe walls, corrugatedsteel pipe has heretofore been unacceptable for use in sanitaryapplications such as sewer drains.

Just as corrugated metal pipe suffers from interior difficulties, aproblem also exists in adequately protecting its external surfaceagainst corrosion. Pipelines are generally laid beneath the ground andagain steel is quite vulnerable to its environment. While plastic andother protective coatings can be applied to the pipe's exterior, asingle holiday in the coating opens the door to damaging corrosion. Thegenerally rough manner in which pipe lengths are handled in the yard,during loading and unloading and on the job, substantially reduces theeffectiveness of these coatings and consequently the advantages ofcorrugated steel pipe as well.

In view of the shortcomings of corrugated metal pipe and concrete pipe,it would be highly desirable to provide a pipe having structural andcost characteristics similar to those of corrugated metal pipe, but withimproved flow characteristics and capable of being readily renderedcorrosive resistant, both interiorly and exteriorly, and, for use insanitary applications, easily provided with a continuously smoothinterior liner. Such pipe could be more economically employed in thoseapplications in which corrugated steel pipe is presently being used andalso would be ideally suited for sewers, storm drains and other areasheretofore outside the field of use of metal corrugated pipe.

SUMMARY OF THE INVENTION

Briefly, the invention comprises a pipe and methods of manufacturingpipe which is hydraulically efficient and adapted for use with interiorand exterior protective coatings. The pipe has a channeled wall defininga hydraulically smooth interior surface and a plurality of eitherannular or helical outwardly projecting structural supporting ribsextending about and along the length of the pipe wall. The channelsformed in the pipe wall interiorly of the supporting ribs are openedalong the interior surface of the pipe to define an anchor throughoutthe length of the pipe for securing thereto a smooth interior lining ofa suitable corrosion resistant protective material.

It is the principal object of the present invention to provide aneconomical and hydraulically efficient pipe which is readily susceptibleof being rendered corrosion resistant.

It is another object of the present invention to provide a metal ribbedpipe having improved fluid flow characteristics over those exhibited bycorrugated metal pipe.

It is a further object of the present invention to provide a metalribbed pipe which includes means integral therewith for anchoring asmooth liner of inert material to the interior of the pipe wall.

It is still a further object of the present invention to provide a metalribbed pipe having an abrasion resistant interior wall surface.

It is yet another object of the present invention to provide a metalribbed pipe which resists damage to external corrosion protectivecoatings applied thereto.

These and other objects and advantages of the present invention willbecome apparent from the following detailed description taken inconjunction with the accompanying drawings.

IN THE DRAWINGS

FIG. 1 is a perspective view of a length of pipe constructed accordingto the present invention.

FIG. 2 is a sectional view taken along line 2--2 in FIG. 1.

FIG. 3 is an enlarged partial sectional view of a length of pipeconstructed in accordance with the present invention and having taperedribs for locking in place an interior liner for use in sanitaryapplications.

FIGS. 4(a) and 4(b) are sectional views of the pipe of the presentinvention having concrete and polymer liners secured theretorespectively.

FIG. 5 illustrates the forming of a length of pipe with an interiorliner therein.

FIG. 6 is a series of sectional views illustrating different ribconfigurations for use in pipe constructed in accordance with thepresent invention.

FIG. 7 is an enlarged sectional view of a portion of a length of pipeconstructed in accordance with the present invention having a smoothinterior liner comprised of abutting. sheets of inert plastic materialanchored to a filler held within the channels in the pipe wall.

FIG. 8 is an enlarged partial sectional view of a length of pipeconstructed in accordance with the present invention illustrating aribbed inner lining tube of inert polymer material anchored within thechannels of the pipe wall.

FIG. 9 illustrates another method for securing a polymer liner to theinterior pipe wall,

FIG. 10 is an enlarged sectional view of a length of pipe constructed inaccordance with the present invention utilizing the lock seam to anchora smooth interior sheet of polymer materials thereto,

FIG. 11 illustrates an alternate embodiment of the present inventionutilizing a perpendicularly disposed lock seam as a structuralsupporting rib and an anchor for an interior liner,

FIG. 12 is an enlarged partial sectional view of a length of pipeconstructed in accordance with the present invention provided withprotective caps for preventing damage to an external corrosionprotective coating,

FIG. 13 is an enlarged sectional view of a length of pipe constructed inaccordance with the present invention utilizing expanded metal betweenthe projecting supporting ribs.

FIG. 14 illustrates a method of forming pipe according to the presentinvention wherein an interior liner is secured to the pipe by the lockseam.

FIG. 15 illustrates the forming of pipe of the present invention whereinreinforcing material is extruded into the formed channels defined by theribs of the pipe.

FIG. 16 illustrates the step of securing an interior liner toreinforcing material disposed in the channel defined by the ribs of thepipe whereby the liner is held secured to the pipe.

FIG. 17 illustrates the process of manufacturing pipe according to thepresent invention wherein the metal between the ribs is expanded and theliner secured to the expanded metal.

FIGS. 18-21 illustrate another embodiment of the present invention andthe method of manufacturing that embodiment.

FIG. 22 is a sectional view of yet another rib configuration for use inpipe constructed in accordance with the present invention.

FIG. 23 illustrates a method of providing the pipe of the presentinvention with longitudinal straightening ribs and FIGS. 23(A) and (B)illustrates two cross-sectional configurations of the straighteningribs.

FIG. 24 is a graph illustrating the relationship between the ratio ofthe spacing between adjacent ribs in the pipe of the present inventionand the width of the channel openings to the coefficient of roughness(n) in Manning's Equation.

FIG. 25 illustrates the forming of an interior liner within a length ofpipe of the present invention by rotational casting.

Referring now in detail to the drawings, the pipe of the presentinvention is preferably constructed from a sheet of steel 11 in varyinggauges, although other materials could be used, and is provided with achanneled cylindrical wall 12 defining a plurality of outwardlyprojecting structural ribs 14 which are preferably uniformly spacedabout and along the length of the pipe. These ribs can either beannularly or helically disposed in the pipe wall although as withconventional corrugated metal pipe, the helical construction ispreferred to facilitate pipe fabrication. While only helically disposedribs are illustrated in the drawings, it is to be understood thatannular ribs could also be employed.

To improve the hydraulic efficiency of pipe 10 over that of corrugatedpipe, the ribs do not cause any inward deformation of the pipe wallthereby providing the pipe with a smooth interior surface 18 of constantradius interrupted solely by flat lock seam 19 which are used to formthe pipe from rolls of sheeting and the spaced channels 20 which formedinteriorly of the ribs 14. As the velocity of fluid flow through pipe 10varies inversely with the roughness factor (n in Manning's Equationabove) which is affected by the ratio of the spacing between channels 20to the width of channel opening (see FIG. 24), this velocity isdependent on this ratio. Within the parameters outlined herein, however,such variance should be relatively slight and the velocity loss due tothe small influence exerted on the fluid flow through the pipe by theopen-spaced channels therethrough are, as noted above, significantlyless than that found in similarly sized corrugated pipe. This differenceresults from the rough sidewalls of the corrugated pipe and theturbulence created thereby as contrasted with the hydraulically smoothinterior surface of pipe 10. Tests conducted on pipe constructed inaccordance with the present invention have determined that with 24 inchdiameter pipe having channels 0.75 inches in height by 0.75 inches inwidth and 12 inch spacings between channels, the roughness factor isabout 0.010 to 0.011. Accordingly, the flow characteristics of such pipeare about the same as those of smooth pipe, superior to concrete pipeand markedly superior to corrugated steel pipe. Due to its improvedhydraulic efficiency, pipe 10 is capable of handling various flowrequirements with smaller diameter pipe than is corrugated pipe therebyrepresenting a significant economic savings.

As the openings 22 of the channels in the pipe wall are reduced in size,the effect of the channels 20 on the fluid flow through the pipe iscorrespondingly reduced and the flow velocity is slightly increased.This is illustrated in FIG. 24 wherein the ratio of the spacing betweenparallel channels to the width of the channel openings is plottedagainst Manning's coefficient of roughness (n). As can be seen therein,this ratio has a critical value beyond which the opening has littleeffect on flow resistence. However, too large a spacing adverselyaffects the strength of the pipe. Tests conducted on pipe 10 indicatethat with channel openings 0.5 to 1.5 inches wide by 0.5 to 1.5 inchesin depth, spaced 6 to 12 inches apart provide excellent structural flowcharacteristics. Tests also demonstrated that spacings of about 11 to 12inches provide excellent hydraulic characteristics. The lower limit onthe spacing between the ribs has yet to be determined. The optimal ribconfiguration to achieve the desired strength and hydrauliccharacteristics is believed to be 0.75 inches wide by 0.75 to 1.0 inchesin depth with spacings of 11-12 inches between the ribs.

Further, various fill heights for both trench and embankmentinstallations were calculated for variations in the dimensions of thechannels, changes in the pitch or spacing between the channels, changesin pipe diameter and the gauge or thickness of the pipe. These fillheights were calculated according to ASTM Standard A796 and are setforth below. These tables show that with a 0.75 inch wide by 0.75 inchdeep rib at a 12 inch pitch (spacing), sheets can be used in 18 and 16gauge thickness for pipe up to 48 and 60 inches in diameterrespectively. With a 0.75 inch wide by 1.0 inch deep rib at an 11 to 12inch pitch, sheets can be used in 18 to 12 gauge thickness for pipe aslarge as 72 to 120 inches in diameter, respectively. These maximumdiameters are for trench installations; maximum diameters for embankmentconditions are somewhat less.

                  TABLE I                                                         ______________________________________                                        Maximum Fill Height (Feet) for Spiral-Rib Pipe                                .75 by .75 Inch Ribs at 12-Inch Pitch                                         Pipe                                                                          Diameter,                                                                     inches         18 Gauge 16 Gauge                                              ______________________________________                                        24             31       44                                                    30             25       35                                                    36             21       30                                                    42             18       25                                                    48             (16)     22                                                    54                      (20)                                                  60                      (18)                                                  ______________________________________                                         *See footnote on page 14                                                 

                  TABLE II                                                        ______________________________________                                        Maximum Fill Height (Feet) for Spiral-Rib Pipe                                .75 by-1-Inch Ribs at 12 Inch Pitch                                           Pipe                                                                          Diameter,                                                                     inches   18 Gauge 16 Gauge   14 Gauge                                                                             12 Gauge                                  ______________________________________                                        24       35       48         68     114                                       30       28       39         54     91                                        36       23       32         45     76                                        42       20       28         39     65                                        48       17       24         34     57                                        54       15       22         30     51                                        60       (14)     19         27     46                                        66       (13)     (18)       25     41                                        72       (12)     (16)       23     38                                        78                (15)       (21)   35                                        84                (14)       (19)   33                                        90                           (18)   (30)                                      96                           (17)   (28)                                      102                                 (27)                                      108                                 (25)                                      114                                 (24)                                      ______________________________________                                         *See footnote on page 14                                                 

                  TABLE III                                                       ______________________________________                                        Maximum Fill Height (Feet) for Spiral-Rib Pipe                                .75 by-1-Inch Ribs at 11-Inch Pitch                                           Pipe                                                                          Diameter,                                                                     inches   18 Gauge 16 Gauge   14 Gauge                                                                             12 Gauge                                  ______________________________________                                        24       38       53         73     123                                       30       30       42         59     99                                        36       25       35         49     82                                        42       22       30         42     70                                        48       19       26         37     62                                        54       17       23         33     55                                        60       (15)     21         29     49                                        66       (14)     (19)       27     45                                        72       (13)     (18)       24     41                                        78                (16)       (23)   38                                                          (15)       (21)   35                                                                     (20)   33                                                                     (18)   (31)                                                                          (29)                                                                          (27)                                                                          (26)                                                                          (25)                                      ______________________________________                                         *(1) Fill heights in parentheses are for trench installations only; other     are for either embankment or trench installations.                            (2) Based on H20 loading, minimum fill height is 1/4 of diameter for pipe     over 48 inches in diameter and 1 foot for all other diameters.           

Testing has shown that these two profiles appear to be essentiallyoptimal over the indicated range of diameters. Other profiles examinedwould not offer significant weight savings for pipe designed for moremoderate fill heights. However, other profiles could be considered forcertain larger diameters. Referring to Table 1, a deeper rib wouldincrease the pipe stiffness and extent the maximum diameters for which18 and 16 gauge sheets could be used, but the maximum fill heights wouldgenerally be reduced because the wall area would not increasesignificantly. The diameters for these sheets gauges could be increasedeffectively by reducing the pitch to 6 inches.

While the above study was based on ribs having vertical sidewalls,slightly tapering the walls to provide tapered channels 20' asillustrated in FIG. 3 should not appreciably affect the structuralsupport afforded by the ribs and slightly reduces the channel openings22' to further improve the hydraulic efficiency of the pipe. Inaddition, narrowing the channel openings forms an anchoring area definedby the tapered channels 20' for Securing an interior or inner liner 28to the inner pipe wall without the need for additional attachment means.A narrowing of the ribs such that the open ends of the channels formedthereby are about one-half or less than the transverse dimension of theouter closed ends of the ribs is ideal for such purposes. By way ofexample, tapering the channels from 0.75 inches at the outer closed end0.375 inches at the open end thereof provides excellent securement ofthe liner. When the pipe 10 is to be used for storm drain applications,a concrete liner if desired would be suitable. The liner could eitherextend about the entire interior of the pipe or solely about the pipe'sinvert or lower surface which is continually subjected to fluid flow. Aconcrete liner is illustrated in FIG. 4(a). In sanitary or sewerapplications an inner lining of inert material such as polyethylene orPVC is preferred due to the effect of sulfuric acid on concrete. Such aliner is shown in FIG. 4(b). It would be noted that such an anchor is ofparticular significance for securing a liner of inert material such aspolyethylene due to the previous inability of the industry tosatisfactorily adhere such a liner to a pipe without additionalattachment means which are often highly susceptible to corrosion anddeterioration. By reducing the size of the channel openings 22' theliner 28 which extends into the channels openings 22' the liner 28 whichextends into the channels is held in place by the necked down channelthroughout the length of the pipe 10. In constructing pipe 10, aconcrete liner would preferably be applied to the interior of the pipeafter fabrication of the pipe and would be firmly held to the pipe wallupon hardening, whereas a polymer liner might more easily be applied tothe interior of the pipe during, fabrication by means of rotationalcasting illustrated in FIG. 25 (to be discussed later herein) or by asuitable. extruding head 30 extending into the interior of the pipethrough the forming end 32 as suggested in FIG. 5. FIG. 5 alsoillustrates the sheet of steel 11 first being directed through a channelformer 27 which forms ribs 14 and then being rolled into a helicalconfiguration just prior to the application of the liner 28.

FIG. 6 illustrates some of the different modifications of the rib shapeswhich could be employed with pipe 10 and provide the desired hydraulicefficiency and structural strength as well as the used rib fillers foradditional strength. FIG. 6(a) illustrates the squared configurationwith tapered rib walls for use in sanitary applications while FIG. 6(b)shows the squared wall design for use in storm drain applications. FIG.6(c) illustrates a rounded rib configuration 34 which, like thatillustrated in FIG. 6(a), provides a bottleneck anchor for an interiorliner. FIG. 6(d) illustrates a rib defining an outwardly taperedchannel. While such a design has a somewhat lower hydraulic efficiencydue to the enlarged channel opening, it employs less material than theinwardly tapered or straight wall configuration and would therefore beeven more economical. In addition, the outwardly tapered channel stillprovides a pipe with a hydraulic efficiency superior to that found incorrugated steel pipe. Accordingly, such a configuration would bewell-suited for certain culvert and other installations not requiringthe use of a durable interior liner but in which some improved hydraulicefficiency would be desired.

FIGS. 6(a-c) also illustrate the use of a structural filler 36 such asconcrete which can be placed within the channels during or following thepipe manufacturing stage to provide a smooth interior surface andadditional structural strength for the pipe 10 without the need foradditional steel thereby resulting in a substantial economic savings.The filler, of course, is anchored within the channel in the same manneras the interior lining 28. It is to be understood that fillers otherthan concrete could be employed for such purpose.

As described above, an inert polymer lining or other interior liners canbe anchored to the interior pipe wall by means of the tapered channels20' to protect the interior of the pipe and provide a continuouslysmooth interior surface for optimal hydraulic efficiency. While FIG.4(b) presently represents the preferred embodiment of the invention foruse in sanitary applications,. FIGS. 7 and 8 illustrate alternativemeans for securing a polyethylene or other inert polymer interior liner28 to the pipe wall. FIG. 7 illustrates pipe 10 having a polyethlyene orother suitable polymer filler 38 disposed within channels 20' and aplurality of abutting sheets of plastic liner rolled into tubes 40 and40' and inserted into the pipe 10 in abutting relationship to define theinterior liner 28. The tubes 40 and 40' are then secured together andthe filler 38 within the channels 20' by means of heat, solvent or othersuitable weld 42 thereby anchoring the interior liner defined by theabutting tubes to the interior pipe wall. This method of securing theinterior liner to the pipe could also be employed with a liner comprisedof a single continuous tube of inert plastic material which extends thelength of the pipe which would be ideally suited for use in shorter pipelengths.

An alternate embodiment, not shown, of securing a liner to an anchorheld within tapered channels 20, employs the use of a cord of materialwhich is held within the channels and which has elongated fibers orstrands of material extending radially therefrom into the interior ofthe pipe 10. The liner is then applied to the interior of the pipe aboutthe fibers or strands such that they become embedded in the liner andthus hold the liner in place against the interior pipe wall.

FIG. 8 illustrates another method for securing a continuous tubeinserted to the interior pipe wall. As seen therein, the plastic tube 44is provided with a plurality of projecting ribs 45 which are pressedinto the channels 20" and held therein by a pressure fit therebyanchoring the tube liner in place. This embodiment differs from thatshown in FIG. 4(b) in that the channels 20" are less tapered thanchannels 20' to accommodate the press fit. Further, the embodimentillustrated in FIG. 4(b) contemplates molding or extruding the linerwithin the tapered channels 20'.

FIG. 9 illustrates another method for securing a plastic liner 28 to theinterior pipe wall wherein the liner is spirally formed into the pipesuch that the location of the seams thereof are disposed over thechannels 20 in the pipe. The ends 50 and 52 of the formed plastic linerare depressed into the channels and are held therein by the force of theplastic filler or plug 48 pressing said ends 50 and 52 against thesidewalls of the rib. If necessary, a solvent or heat weld could beapplied at the junctures of the formed liner 46 and the filler or plug48.

FIG. 10 illustrates another use of the invention wherein a flat lockseam 54 of the pipe, which extends helically about and along the pipebetween the projecting ribs and which is employed to form the pipelength from a sheet of flat metal, is also employed to anchor aninterior plastic liner 28 to the interior pipe wall 12. Lock seam 54differs from the conventional lock seam used in the manufacture ofspiral pipe in that the seam is pressed flat to maintain a flat surfacebetween the projecting ribs and avoid any adverse effects on the fluidflow characteristics of the pipe. A sheet of polymer material 56 havinga width the same as that of the metal sheeting from which the pipe isfabricated after the ribs have been formed therein is spirally fed intothe pipe during the fabrication thereof and the lateral ends 58 and 60of the sheet are pressed into the forming lock seam and held therein bythe resulting pressure fit. In this method of construction the sheet ofpolymer material has a width the same as that of the metal sheeting fromwhich the pipe is fabricated with the ribs formed therein. In thismanner the lateral edges of the liner are aligned with the metalsheeting and upon joining these edges together in a lock,seam, the pipe10 is provided with a smoother interior liner interrupted solely by theindentations 62 under the spiralling lock seam. The smooth, flat portionof the pipe wall between the channels 20 therein provides support forthe inner liner and prevents the liner from being pressed into acorrugated configuration under the force of the flow therethrough whichotherwise would result were such a locking process to be employed withcorrugated steel pipe.

A variation of the above implementation of the lock seam of the pipe asan anchor for an interior liner is illustrated in FIG. 11. As showntherein, the lock seam 64 is raised to a perpendicular disposition withrespect to the longitudinal axis of the pipe 12 so that the seam itselfprovides the necessary strength for the pipe and the ribs and openchannels 20 defined thereby have been eliminated. This embodiment issuited for smaller diameter pipe (about 6 to 18 inches in diameter)where less structural supporting strength is needed. By perpendicularlydisposing the lock seam with respect to the pipe, the lock seam itselfdefines a supporting rib which acts both to support the pipe and anchoran interior liner in the manner just described.

In addition to greatly increasing the hydraulic efficiency of the pipe10 and providing an anchor for securing a protective liner to theinterior pipe wall, the protruding structural ribs 14 can also serve toprotect the pipe's exterior. FIG. 12 illustrates a pipe 10 provided withan external corrosion-resistant coating 68 which is shown in FIG. 5being extruded Unto the pipe through forming head 66. To protect thiscoating, a corrosion resistant durable metal cap 70 is secured about theextended end 72 of the rib and affixed thereto by a suitable adhesive.As the rib spacing on pipe 10 is rarely greater than 12 inches (seeTable 3), a plurality of such caps disposed over the protruding ribsshould provide excellent protection for the relatively fragile coating68 as pipe lengths are knocked together in the yard, during thetransport and on the job. The interior protective liner 28 illustratedin FIG. 12 is of integral construction such that a portion 28' thereofprojects into and is anchored within the channel formed by ribs 14, Themethod by which liner 28 could be applied to the pipe wall isillustrated in FIG. 5,

Another embodiment of the present invention is illustrated in FIG. 13.This embodiment differs from the preferred embodiment in that theportion 74 of the pipe wall extending between the parallel ribs 14 isformed of expanded metal. The process for forming such pipe isillustrated in FIG. 17, As seen therein, the metal sheet 11 is passedthrough a channel former 27 for forming channels 20 and projecting ribs14, The sheet then is passed through an expander 86 which slits themetal in portion 16 on either side of the channels and expands the metallaterally and vertically to define what is commonly termed expandedmetal. In such an embodiment, excess material for the formation of theribs and lock seams becomes available throughout the expansion ofportion 16 and the expanded portion 16 which extends in both verticaldirections from an otherwise flat surface defines a key which acceptsand itself becomes an anchor for a smooth protective coating 76. Thiscoating extends both internally and exteriorly of the pipe wall andthereby protects the pipe from both internal and exterior corrosion.Such a coating could be extruded onto a limited area of the pipe eitherduring or after fabrication thereof and as the pipe was rotated andlinearly moved with respect to the extruding head, an even coating wouldbe applied to the forming or formed pipe which would form both aninterior and exterior lining of unitary construction. Such a liningcould either be of a polymer material, portland cement mortar for stormdrain uses, a polymer concrete or other inert material suitable forproviding the desired protective lining. FIG. 17 illustrates the coating76 being applied by extruding head 87.

FIG. 14 illustrates the forming of pipe 10 wherein the liner 28 isdisposed over the sheet of steel 11 with channels 20 formed therein suchthat the lateral edges 28" of the liner are disposed over and adjacentthe lateral edges 11' of the steel sheet 11. So positioned, the sheetand liner are rolled into a helical configuration defining a length ofpipe with a plurality of outwardly projecting ribs 14, an interior liner28 and a helically extending seam 53. The seam 53 is defined by theadjacent lateral edges 28" and 11' of the liner and sheet of steel.These edges are then pressed together to form the lock seam 54illustrated in FIG. 10, thereby locking and maintaining the interiorliner 28 in place.

FIG. 15 illustrates the forming of pipe 10 wherein the sheet of steel 11is first directed through the channel former 27 for forming the channels20 and projecting ribs 14. The formed sheet is then rolled into ahelical configuration to define a length of pipe having a plurality ofoutwardly projecting ribs 14 and a corresponding plurality of helicallydisposed channels 20 on the interior of the pipe. A reinforcing material38, preferably a polymer filler, is then placed with the channels by anextruding or any other suitable means generally designated 82. A polymertube 40 defining an interior liner is then placed within the pipe andsecured to the filler material 38 held within the pipe channels 20 bymeans of a heat, solvent or other suitable weld 42 which could beapplied by welding means 84. As described above, and as illustrated inFIGS. 7 and 16, either a single or a plurality of liner tubes 40 can bedisposed within the pipe with the abutting ends of the tubes beingsecured together and to the filler material 38 within the channels 20 bythe same weld. The use of a plurality of such tubes, of course, ispreferable when forming longer pipe lengths.

FIGS. 18-21 illustrate yet another embodiment of the present inventionand the method for making the same. In this embodiment, a sheet of steel11 is directed through a flanging device 90 which bends the lateraledges of the sheet slightly over 90 degrees downwardly to form flanges92. The sheet is then rolled into a helical configuration to define thepipe length. As the pipe length is being formed, an elongated formed rib94 is directed over the adjacently disposed flanges 92 and is rolledinto a helix about the flanges. The legs 96 of the ribs are then pressedinwardly by rollers 98 of pressing member 100 to secure together theadjacent flanges of the helical shape and form the pipe length. Thismethod is illustrated in FIGS. 20 and 21 and the resulting pipe is shownin partial cross-section in FIG. 18. It should be noted that theinterior spacing 102 under the rib 94 about the flanges could be filledwith a filler material 104 such as polyurethane foam for protectionagainst corrosion and the provision of a watertight seal, as shown underone portion of the rib in FIG. 18. FIG. 19 illustrates the use of thisembodiment of the invention with an interior liner 28 held against theflanges 92 by rib 94 as well as an outer protective coating 68 which, asdiscussed above, could be extruded onto the pipe as shown in FIG. 5.

FIG. 22 illustrates yet another embodiment of the invention which issomewhat similar to the upstanding lock seam illustrated in FIG. 11. Inthis embodiment, however, the rib 110 is defined by a channel member 112preferably formed of about 14 gauge steel and which is slightly bent atits mid-point 114 and is provided with inwardly facing hook portions 116at the ends thereof. In constructing this embodiment of applicants'pipe, a liner 28 is disposed over the sheet of steel 11 such that thelateral edges of the liner are disposed over and adjacent to the lateraledges of the steel sheet as seen in FIG. 14. The lateral edges 11 and11' of the sheet and liner are then rolled together by a suitable formerto define channel hooks 118. The sheet and liner are then rolled into ahelical configuration and the channel member 112 is directed over thethen adjacently disposed channel hooks and rolled into a helix in thesame manner as rib 94 in the embodiment illustrated in FIG. 19. The endsof the channel member 112 are then pressed inwardly as shown in FIG. 22such that the hook portions 116 thereof interlock with the channel hooks118 on the channel member 112 thereby securing together the lateraledges of the steel sheet 11 and liner 28 and forming the pipe section.As with the prior embodiment, a filler material can be injected into thespace 120 formed by the channel member 112 above the interlocking endhooks 116 and 118.

In addition to providing the pipe 10 with an inert liner by means ofextrusion as illustrated in FIG. 5, such a liner could also be securedby rotational casting. The use of conventional rotational casting toform the liner would comprise the steps of plugging the ends of the pipe10 to effectively form a die with a charging hole for material, chargingthe interior of the pipe with a polyethylene, PVC or ABS powder throughthe hole, placing the pipe in an oven, heating the oven to about 520°Fahrenheit and, while in the oven, both rotate the pipe about itslongitudinal axis and rock the pipe about a transverse center horizontalaxis in a teeter-totter like motion. The rotation and rocking of thepipe evenly distributes the powder about the interior of the pipe whichthen sets up against the interior pipe wall and is held in place by thatportion of the formed liner which is disposed within the taperedchannels 20'. Such a process, however, contains certain drawbacks. Theequipment for creating the rocking motion would be bulky and expensivein that it would have to withstand the high curing temperatures withinthe oven and, due to the rocking motion, would necessarily provide thepipe with polymer end caps which would have to be cut away. Analternative method which utilizes the rotational casting concept isillustrated in FIG. 25.

As seen in FIG. 25, the pipe 10 is provided with end plugs 150, one ofwhich has a tube 152 of about 10 inches in diameter extendingtherethrough and along the interior length of the pipe. The relativelylarge diameter of the tubing allows the tubing to be insulated bysuitable material 153 and/or fluid cooling so as to withstand thetemperatures within the oven. Tubing 152 is also provided with aplurality of openings or nozzles 154 equally spaced longitudinally alongthe length thereof for discharging the powder of polymer against theinterior pipe wall. The pipe 10 is supported on a roller assembly 156for rotating the pipe about its center longitudinal axis within oven156. With the oven at a temperature of about 520° Fahrenheit, thepolymer powder is charged through the tube 152 and out nozzles 154 ontothe interior pipe wall. As the powder passes through the tube 152, thepipe is rotated on the roller assembly 156 to provide an evendistribution of the powder along the interior of the pipe wall. Theliner then sets up within the oven as discussed above.

Each of the aforesaid embodiments of the present application provides apipe which is not only more hydraulically efficient than conventionalcorrugated pipe but is readily adapted for having secured thereto aninert interior liner to resist corrosion.

If desired, the pipe 10 of the present invention as shown in FIG. 23 canhe further strengthened by the addition of longitudinal stiffening ribs122 which, while adding strength to the pipe, will not adversely affectthe hydraulic efficiency and, in fact, may increase the efficiency asthe added strength supplied by the stiffening ribs would allow theadjacent channels defined by the helical rib to be spaced further apartthereby increasing the velocity of fluid flow as illustrated by thegraph shown in FIG. 24 and Manning's Equation. FIG. 23 illustrates theforming of ribs 122 which are formed in the steel sheet 11 by flyingpress dies 124 or other suitable means after the sheet passes throughthe channel former 27. In this manner, the ribs can be added withoutslowing the manufacturing process. FIGS. 23(A) and 23(B) illustratealternative cross-sections for stiffening ribs 122.

Various other changes and modifications may be made in carrying out thepresent invention without departing from the spirit and scope, thereof.Insofar as these changes and modifications are within the purview of theappended claims, they are to be considered as part of the presentinvention.

We claim:
 1. A hydraulically efficient underground pipe formed of singlepiece metal wall construction for use in buried storm drainapplications, said pipe comprising:a cylindrical metal wall; a lock seamextending helically about and along the length of said wall; a pluralityof outwardly projecting ribs extending helically about and along thelength of said wall and being integrally formed therewith, said ribsdefining a corresponding plurality of open channels being adapted torender the pipe substantially rigid so as to possess sufficientstructural strength to withstand the stresses of being buriedunderground, said metal wall including a plurality of openings formedtherein between said ribs; and a liner extruded onto the interior ofsaid metal wall.
 2. The hydraulically efficient underground pipe asrecited in claim 1 wherein said openings are defined by expanding saidmetal wall between said ribs.